In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been the control of the printing operation. As is well-known, the impact operation depends on the movement of impact members such as wires or the like and which are typically moved by means of an electromechanical system which is believed to enable a more precise control of the impact members.
The advent of non-impact printing, as in the case of thermal printing, brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing in at least one form thereof must deal with rapid starting and stopping movement of the ink fluid from a supply of the fluid. In each case, the precise control of the thermal elements and of the ink droplets is necessary to provide for both direct and high-speed printing.
In the matter of ink jet printing, it is extremely important that the control of the ink droplets be both precise and accurate from the time of formation of the droplets to the depositing of such droplets on paper or like record media. While the method of printing with ink may be performed in continuous pulse manner or in pulse on demand manner, the latter method is disclosed in the present application as applying the features of the present invention. The drive means for the ink droplets is generally in the form of a crystal element to provide the high-speed operation for ejecting the ink through the nozzle while allowing time between droplets for proper operation.
It is therefore proposed to provide means for driving the ink to maintain high-speed ink jet printing wherein the deflection of the ink occurs at a time prior to ejection through the ink nozzle.
Representative prior art in the field of method and apparatus for ink jet printing in continuous manner includes U.S. Pat. No. 3,769,624, issued to C. H. Lee et al. on Oct. 30, 1973, which discloses a system projecting a stream of writing fluid in the form of uniformly spaced and equally-charged droplets which are then electrostatically deflected a dependent amount after passing through the ink jet nozzle.
U.S. Pat. No. 3,798,656, issued to P. Lowy et al. on Mar. 19, 1974, discloses an ink return system for a multi-jet printer which has deflection plates either at a positive or a negative potential and which includes catch chambers mechanically biased and positioned at a slight angle for receiving uncharged droplets from the nozzles.
U.S. Pat. No. 3,805,272, issued to G. J. Fan et al. on Apr. 16, 1974, discloses an ink jet recording system having means for producing a stream of ink droplets and magnetic deflection means including two spaced pole pieces forming an air gap therebetween and located beyond the nozzle for receiving the stream of droplets.
U.S. Pat. No. 3,852,768, issued to J. M. Carmichael et al. on Dec. 3, 1974, discloses a method of detecting charges on drops in an ink jet stream without contacting the stream and which includes determining the charging, the velocity of the ink stream, the extent of deflection of the ink drops originating from a nozzle and whether or not the ink stream is in operation.
U.S. Pat. No. 3,877,036, issued to K. H. Loeffler et al. on Apr. 8, 1975, discloses an ink jet printer having an electrode by the continuous stream of ink being emitted by the jet and applying a voltage so as to create an asymmetrical force field which has a component perpendicular to the ink stream direction and which affects the trajectory of the stream by deflection thereof.
And, U.S. Pat. No. 3,878,518, issued to R. L. Garwin on Apr. 15, 1975, discloses method and apparatus for amplifying the deflection of a droplet of a liquid magnetic stream wherein a static magnetic field is applied by separate deflection means which is synchronized with the formation of the ink droplets.